REPAIR OF DNA-PROTEIN CROSS-LINKS IN AN EXCISION REPAIR-DEFICIENT HUMAN CELL-LINE AND ITS SIMIAN-VIRUS 40-TRANSFORMED DERIVATIVE

Abstract

DNA-protein cross-links are induced in mammalian cells by X-rays UV light, fluorescent light and numerous chemical carcinogens. These cross-links are repaired by normal cells, but excision repair-deficient xeroderma pigmentosum (XP) Group A cells, XP12BE, are deficient in repair of these bulky adducts. The DNA-protein cross-link repair competency of another XP Group A strain, XP20S, was compared with its more rapidly proliferating SV40-transformed derivative line and with normal human skin fibroblasts. DNA-protein cross-links were induced with 20 .mu.M trans-platinum(II)diamminedichloride and assayed by the membrane alkaline elution procedure of Kohn. Treated and untreated cells are lysed on a polycarbonate membrane filter, and the coelution rates of the DNA at pH 12.2 are compared; DNA-protein cross-links retard elution of DNA. The repair competency of XP20S cells for trans-platinum(II)diamminedichloride-induced DNA-protein cross-links was similar to that of XP12BE cells, but the competency of the SV40-transformed XP20S cells was nearly equal to that of normal human skin fibroblasts. Either cell cycling compensates for the genetic deficiency present in the nucleotide excision process of XP Group A cells or a process other than nucleotide excision can repair these lesions; this process requires cell cycling or activation by the virus.